1. CONSTRAINTS FROM RGM MEASUREMENTS ON GLOBAL MERCURY CHEMISTRY Noelle Eckley Selin 1 Daniel J. Jacob 1, Rokjin J. Park 1, Robert M. Yantosca 1, Sarah Strode, Lyatt Jaegle, Daniel Jaffe 1 Harvard University Department of Earth and Planetary Sciences Atmospheric Chemistry Modeling Group Mercury 2006 Madison, WI, USA 10 August 2006

2. MERCURY IN THE ATMOSPHERE Hg(0) Hg(II)Oxidation OH, O 3, Br(?) GAS PHASE AQUEOUS PHASE SOLID PHASE TOTAL GASEOUS MERCURY (TGM) DRY AND WET DEPOSITION REACTIVE GASEOUS MERCURY (RGM) RELATIVELY INSOLUBLE ATMOSPHERIC LIFETIME: ABOUT 1 YEAR TYPICAL LEVELS: 1.7 ng m -3 LIFETIME: DAYS TO WEEKS TYPICAL LEVELS: 1-100 pg m -3 Reduction Photochemical aqueous (?) Hg(II)Hg(P) ECOSYSTEM INPUTS VERY SOLUBLE

3. Hg(0) 4500 (3900) Hg(II) 860 (300) OH:12000 Dry deposition Land (primary) emission Anthropogenic emission Land re-emission Hg(P) 1.9 (1.9) 700 200 O3:2400 1500 1300 500 2800 Dry deposition Wet deposition 4700 2100 19010 hv (cloud):8300 Ocean emission MERCURY BUDGET IN GEOS-Chem Inventories in Mg (Troposphere in parentheses) Rates in Mg/yr

4. CONSTRAINTS FROM ANNUAL MEAN MEASUREMENTS + TGM Average concentration at 22 land-based sites Measured: 1.58 ± 0.19 ng/m3 Simulated: 1.63 ± 0.10 ng/m3 High Atlantic cruise data? Hg(II)+Hg(P) Average simulated concentrations over continents: 17-47 pg/m3 Consistent with measurements High values over poles where reduction suppressed Low values over oceans: fast sink due to uptake by sea salt [Selin et al. 2006, JGR]

5. CONSTRAINTS FROM TIME SERIES AT OKINAWA [Selin et al. 2006, JGR] Observed (Jaffe et al., 2005) Model CO correlated with Hg(0), but not with RGM Implies Asian source (underestimated by 30% in the model) Model captures day-to-day variations in CO, Hg(0), RGM RGM diurnal variation (next slide); Day-to-day variation of RGM driven by suppression of dry deposition

6. OKINAWA CONTINUED: SEA-SALT SINK? Previous GEOS-Chem vs. measurements at Okinawa by Jaffe et al. (2005): model overestimates measurements by a factor of 3 (note difference in scale), but captures some day-to- day variation in observations Revised Model and measured RGM including an implied sink for RGM (sea salt uptake?) are consistent with order of magnitude of Okinawa observations (same scale)

7. DIURNAL CYCLE OF RGM AT OKINAWA Observations Model Diurnal cycle of RGM at Okinawa: morning increase (photochemical production) fast sink (propose uptake onto sea-salt aerosol) von Glasow et al., GRL 2002 OH Br Production Rate Typical diurnal variation of OH and Br [Selin et al. 2006, JGR]

8. A HIGH-ALTITUDE RGM SOURCE? Measurements of RGM at Mt. Bachelor, Oregon (2.7 km) show elevated levels relative to surface measurements mean 43 pg m -3 [Swartzendruber et al. 2006, JGR, submitted] [Selin et al. 2006, JGR] Vertical distribution of Hg(0) mixing ratios near southern Japan. Observations from the ACE-Asia aircraft campaign in April-May 2001 [Friedli et al., 2004] Observations Model Hg(II) Hg(0)

9. CONSTRAINTS FROM TIME SERIES AT MT. BACHELOR, OREGON Measurements of RGM at Mt. Bachelor, Oregon (2.7 km) show elevated levels relative to surface measurements mean 43 pg m-3 Model does not capture episodes of very high RGM [Swartzendruber et al. 2006, JGR, submitted] Vertical profile of GEOS-Chem vs. measurements at Mt. Bachelor ▲ =daytime ● (blue)=all ◊ = nighttime

10. DEPOSITION: LOCAL VS. GLOBAL SOURCES Two patterns of mercury wet deposition over the U.S. (background=model, dots=measured) 1)Latitudinal gradient (higher in warm, sunny, wet places, e.g. Florida, Texas). From oxidation of global pool of Hg(0) and subsequent rainout 2)Near-source wet deposition of locally-emitted Hg(II) and Hg(P) (underestimated in GEOS-Chem) Measurements [Mercury Deposition Network, 2006]; GEOS-Chem [Selin et al. 2006] % contribution of North American sources to total (wet + dry) deposition GEOS-Chem model U.S. mean: 20% Reflects influence of locally-deposited Hg(II) and Hg(P) in source regions

11. Acknowledgments This work was funded by the Atmospheric Chemistry Program of the U.S. National Science Foundation, by a U.S. Environmental Protection Agency (EPA) Science to Achieve Results (STAR) Graduate Fellowship to NES, and by the EPA Intercontinental Transport of Air Pollutants (ICAP) program.